For a moving object such as a smart munition to be guided or its motion altered or controlled, the control system that provided guidance and control action must have real-time information about the position and orientation of the object. In general and depending on each specific application, the position and orientation may be those of the moving object relative to a ground station, or relative to another moving platform.
To meet the requirements of the U.S. Army's future needs in the areas of precision-guided direct- and indirect-fire munitions, it is important that the position and orientation sensors be capable of being integrated reliably and economically into small- and medium-caliber munitions as well as long-range munitions. In particular, it is desirable to embed such sensors in the munitions, and that the sensors be autonomous and provide onboard position and orientation information relative to a ground station or other moving platforms.
Currently, radar-based guidance, often augmented by Global Positioning System (GPS) data, is used to determine information related to the position of munitions. Radar-based guidance of munitions is based upon the use of radio frequency (RF) antennas printed or placed on the surface of munitions to reflect RF energy emanating from a ground-based radar system. The reflected energy is then used to track the munition or the stream of bullets on the way to the target. The surface printed or placed antennas are, however, not suitable for munitions applications since they cannot survive the firing environment and readily loose their accuracy. Such surface printed or placed antenna based sensors also require large amount of power for their operation, and are very sensitive to geometrical variations and tolerances.
Corrections to a munition's flight path are currently possible but only if the munitions are equipped with an additional suite of internal sensors such as Inertia Measurement Unit (IMU's), accelerometers, and gyroscopes. Global Positioning Signals (GPS) are also used alone or in combination with other sensors such as accelerometers and gyroscopes. However, such inertia-based sensors are relatively complex and inaccurate, occupy a considerable amount of volume, consume a large amount of power, are prone to drift and settling problems, and are relatively costly. The GPS sensors cannot provide orientation information and are prone to the loss of signal along the path of travel.
Furthermore, the current IMU technology cannot be implemented for munitions that are subjected to extremely high acceleration rates during firing, such as medium and small caliber munitions. High performance munitions may be subjected to accelerations in excess of 100,000 Gs. In general, inertia based sensors have not been successfully developed to survive firing accelerations of 30,000 Gs and over and also be capable to have measurement sensitivity to measure low acceleration levels required for guidance and control purposes.
It is readily appreciated by those skilled in the art that the issues and concerns described above for munitions are generally true for all mobile platforms.
A need therefore exists for position and orientation measurement systems (sensors) in general, and for those that could be mounted or embedded into various moving platforms for their guidance and control. In munitions applications in particular, the full position and orientation (pitch, yaw and roll) information defines the motion of munitions in-flight and allows it to be guided towards its target.
Furthermore, to guide a moving object along a desired trajectory, the object must be equipped with internal sensors to provide its position and/or orientation to the control system to generate an appropriate control signal, preferably as feedback in a closed-loop control, to keep or guide the object towards the desired trajectory within a certain margin of error. The most common position and/or orientation measurement sensors include various accelerometers and gyroscopes. Magnetometers have been used mostly to determine orientation of the object relative to the ground (usually called roll). Alternatively, the position and/or orientation sensory information may be provided by an external means such as a GPS system. Global Positioning Signals (GPS) are used particularly to obtain position information. Alternatively, the methods and systems disclosed in U.S. Pat. No. 6,724,341 and discussed briefly below could be used.
Hereinafter, path and position are intended to indicate orientation as well, noting that a rigid object requires three independent position information and three independent orientation information to uniquely specify its position and orientation in an appropriate reference system.
In a similar manner, guidance and control of munitions in flight is possible only if the munitions are equipped with a suite of internal sensors such as Inertia Measurement Unit (IMU's), accelerometers, gyroscopes, magnetometers and/or Global Positioning Signals (GPS). In general, more than one of the above sensors are required to obtain full position and orientation information onboard an object, including munitions. Alternatively, the methods and systems disclosed in U.S. Pat. No. 6,724,341 could be used.
The shortcoming of the inertia based sensors, including drift and noise, are described in U.S. Pat. No. 6,724,341. The magnetometers are generally not very sensitive for accurate roll measurement and respond to large nearby masses. The GPS sensors cannot provide accurate orientation information and are prone to the loss of signal along the path of travel. These shortcomings are important to all moving objects, but are particular important to guided munitions, including gun-fired projectile, mortars, sub-munitions, rockets and bombs. In addition, inertia based sensors occupy a considerable amount of volume, consume a large amount of power, are prone to drift and settling problems and are relatively costly. The methods and systems disclosed in U.S. Pat. No. 6,724,341 are shown to overcome the aforementioned shortcomings of the currently available sensors for use onboard moving objects in general and onboard munitions in particular.
During engineering development and testing of remotely controlled, autonomous, guided robotic mobile platforms, gun-fired guided munitions, rockets, unmanned aerial vehicles (UAV), unmanned guided floating and submerged platforms, and other similar moving objects and/or platforms, the development, testing and performance evaluation personnel and teams need to have the means to determine and validate the performance of the overall system and its various components as well as the of their guidance and control algorithms and software. Such guidance and control system and component hardware and software testing capability is essential for the design and development engineers to validate and/or modify their computer models and other formulations and calculations, to evaluate and test various components under operating conditions, and to evaluate and modify and/or debug their control algorithms and software, etc. This capability is also essential for testing and validating the performance of the final product.
Another objective of the present invention is to provide a method and means of determining and/or validating the performance of the guidance and control system of a guided object and its various hardware and software components.